Binders for foundry molds and cores



BENDERS FOR FOUNDRY MOLDS AND CORES Burgess P. Wallace, Brooklyn, Van Dyke Romne Meiers Corners, and Heinz H. Becker, Forest Hills, N. Y., as signers to Whitehead Brothers Company, New York, N. Y.,' a corporation of New Jersey No Drawing. Application May 5, 1955 Serial No. 506,378

6 Claims. (Cl. 10638.8)

This invention relates to the treatment of pitch and petroleum asphalt resins to develop therein characteristics which render the same peculiarly adapted for use in making binders for foundry molds and cores.

Among the principal objects of the invention are the production of cheap binders containing both coal tar pitch and petroleum asphalt resins which possess remarkable and uniform strength that is developed in but a fraction of the baking time required for ordinary binders now in use and which binders, when incorporated in foundry cores, impart thereto the property of ready removability from castings formed in molds in which such cores have been inserted.

It has been acommon practice for many years in the foundry industry to utilize in the manufacture of cores a binder constituting a coal tar pitch of a softening point between about 285 F. and 315 F. (Ring and Ball method) and having a volatiles content ranging from about 40% to 60%. Pitch of this description has come to be known as foundry pitch as it is the only type of coal tar pitch which will not recoalesce after it has been reduced to 100 mesh size. This pitch when used as a binder for cores and molds developed variable strengths because, depending on its spreading and solidifying characteristics, it will harden into a very porous structure somewhat similar to a honeycomb. The degree of porosity produced on solidification would vary from one batch to am other. It is evident that with a binding structure that varies from core to core or mold to mold that the core or mold strength would consequently vary over a wide range.

The coal tar pitch commonly used as a binder for refractory grains, such as silica sand, olivine and like refractory oxides, is first pulverized and then mixed with such refractory grains in the proportion of 1 to 3 parts of the pitch to about 89 to 94 parts of the refractory grains, which latter are sharp when used in making cores and clay-bonded when use in making molds. To the foregoing mix A to 2 parts of dextrine, cereal binder or the like, admixed with about 4 to 6 parts of water, are then added and the resultant mix is then shaped into the desired contours and baked at a temperature of from 300 F. to 900 F. for a period of between about 10 and 60 minutes per inch of radius of the shaped mass. In the case of cores, the baked shape will have a compressive strength of from 70 to 300 lbs. (p. s. i.) for a mix in which the pitch bond is about 3% of the entire mass.

A core produced as just described possesses several serious disadvantages, among which are the inability to obtain an even strength from core to core and the fact that after the metal has been poured around such pitchbonded core, in a mold with its limited supply of oxygen, the pitch forms with the sand of the core a hard mass or structure the removal of which is a difficult matter. Still another serious and expensive disadvantage resides in the aforesaid excessive length of baking time of from 10 to 60 minutes per inch of radius required to develop the maximum pitch strength in cores bonded therewith.

2,863,781 Patented Dec. 9, 195's Our investigation has shown that petroleum asphalt resin, when used in place of coal tar pitch, has such a short life in the foundry at core-baking temperatures, that the outside of the core will be seriously damaged by overbaking before the inside or center of the core is cured or properly baked. Moreover, petroleum asphalt resin cannot be shipped as a fine powder because, after it has been reduced to a fine subdivision it will, on standing, coalesce or revert to its original solid condition. However, since in the hardening of the asphalt resin in the baking stage, under the influence of heat, the structure of the infusible mass so produced has a denser structure than the infusible mass produced by coal tar pitch which has been subjected to the same conditions, the cores made with an asphalt resin binder and refractory grains therefore have more uniform strength.

When petroleum asphalt resin and coal tar pitch are melted together they will not form a homogeneous liquid for neither will dissolve in the other regardless of the amount of stirring that is employed. When these liquids are allowed to cool and re-solidify they willagain form discrete solids. If these solid materials are now ground together they will form a system of randomly distributed particles of coal tar pitch and petroleum asphalt resin. In cores and molds bonded by the resulting mixture and baked, the two solids, on melting, will not mix and the pitch-asphalt resin mix will behave as if they were two separate binders. Further, the pitch will go through the same cycle as if the asphalt resin were not present. The maximum strength of the pitch bond will occur at a given time depending on the temperature, and the maximum strength of the asphalt resin will occur at another time, also depending on the temperature. However, the two materials will never develop their strength simultaneously so that the strength developed in a mold or core will be as if only pitch were present at one time, and as if only asphalt resin were present at another time. Since the two materials are used together and both develop their own strength at dififerent times, it will be as if the cores were bonded by a percentage of pitch that is equal to the percentage in the admixture of pitch-asphalt resin multiplied by the percentage used in the mold or core mix at one time and the same for the asphalt resin at another time. Accordingly, at no time will the mold or core have the maximum strength which is obtainable were both to attain maximum strength simultaneously. 7

Our invention stems from the discovery that two immiscible non-compatible binders can be caused to form a single new substance by supplying co-po-lymers which, on polymerization, form' a compatible reactive substance.

If coal tar pitch, petroleum asphalt resin, the solid content of bi-sulphite waste liquor and resorcinol are mixed' together and melted one obtains a polymerized homogeneous substance or mix that has a characteristic temperature range within which the substance softens to a liquid at one end of such range and hardens to a solid at its other end. Moreover it is within such temperature range that the maximum strength of the said substance is achieved. When this mix is pulverized and admixed with sand or other refractory grains in the proportion of from to 15% binder to 99 /2% to refractory grains with added cereal, dextrine or other commonly used adhesive plus water, and the mass made into molds or cores in the usual manner, then molds or cores, having totally novel and completely unexpected attributes, result. The strength developed in molds or cores prepared with our improved binder is three times as great as that developed by a pitch binder.

alone and twice as great as that strength developed by a petroleum asphalt resin alone. The structure developed after the mix has been brought to an infusible condition by heat is a dense non-porous structure so that uniform core strength develops from shape to shape. That is, the strength is reproducibile. The core is easily removed from the casting after it has served its purpose, since then the retained strength of the core is very small. The baking time required for a mold or core to attain its maximum strength is reduced to V5 that of pitch alone.

In carrying out the production of our improved binder, it is preferable to proceed as follows: 2 /2 tons of petroleum asphalt resin (liquefied by heat), characterized by a softening point of 285 F. to 305 F. and a penetration number of at 77 F. with a load of 100 grms. for 5 sec. and 60% to 80% volatile matter (A. S. T. M. Standard D--271-48) are admixed with 2 tons of liquid coal tar pitch characterized by a melting point (R & B) of 285 F. to 315 F.; penetration number (at 77 F. with a load of 100 grs. for 5 seconds)0; and volatile matter 40% to 60%, 500 lbs. of powdered rcsorcinol and 500 lbs. of dry sulphite waste liquor are then added to the mixture of asphalt resin and pitch and the resulting mass is heated, with constant stirring, to a temperature of from 300 F. to 325 F. for a period of about one hour. The mass is then allowed to cool until it solidifies, whereupon it is reduced to about 100 mesh in fineness by grinding the same. The resulting binder is used in the conventional manner to prepare molds and cores.

The following tabulation shows the strength developed at 700 F., of coal tar pitch, alone, petroleum asphalt resin, and our Improved Binder.

Comparison of binder strengths developed at 700 F.

Baking time in minutes 15 30 l 60 9O Strengths developed in p. s. t. by the follow- I ingr substances:

Coal 'lar Pitch 100 137 230 191 Petroleum Asphalt Resin 282 247 21 8 Improved Binder 512 302 307 20 The percentages of the various components of our improved bituminous binder, based on the total weight of the latter, may vary as follows:

Various modifications of the invention embraced within the scope of the method and product claims 4 presented or which may hereafter be presented herein, may be made without departing from the spirit of our invention.

Having thus described the invention, what we claim and desire to secure by Letters Patent is:

l. The method of making a bituminous binder for foundry molds and cores, which comprises forming a mix consisting essentially of 40 to percent of petroleum asphalt resin, by weight, 30 to 55 percent of coal tar pitch, by weight, 3 to 8 percent of resorcinol, by weight, and 3 to 10 percent of the solid content of bisulphite waste liquor, by weight, maintaining the resultant mix at a temperature of between 300 and 325 F. for at least /2 hour, then allowing the resultant mass to cool and reducing the same to a powder.

2. The method of making a bituminous binder for foundry molds and cores, which comprises forming a mix consisting essentially of 45 to 55 percent of petroleum asphalt resin, by weight, 45 to 55 percent of coal tar pitch, by weight, 4 to 6 percent of resorcinol, by weight, and 4 /2 to 5 /2 percent of the solid content of bi-sulphite waste liquor, by weight, maintaining the resultant mix at a temperature of between 300 and 325 F. for at least /1 hour, then allowing the resultant mass to cool and reducing the same to a powder.

3. The method of making a bituminous binder for foundry molds and cores, which comprises forming a mix consisting essentially of 50 percent of petroleum asphalt resin, by weight, 40 percent of coal tar pitch, by weight, 5 percent of resorcinol, by weight, and 5 percent of the solid content of bi-sulphite waste liquor, by weight, maintaining the resultant mix at a temperature of between 300 and 325 F. for at least /2 hour, then allowing the resultant mass to cool and reducing the same to a powder.

4. A bituminous binder for foundry molds and cores prepared in accordance with the process of claim 1.

5. A bituminous binder for foundry molds and cores prepared in accordance with the process of claim 2.

6. A bituminous binder for foundry molds and cores prepared in accordance with the process of claim 3.

References Cited in the file of this patent UNITED STATES PATENTS 1,221,259 Woddrop Apr. 3, 1917 2,469,908 Wallace May 10, 1949 2,558,402 Wallace June 26, 1951 2,686,728 Wallace Aug. 17, 1954 OTHER REFERENCES Abraham: Asphalts and Allied Substances (pub. 1920 by Van Nostrand) (pp. 226-227).

Sutermeister: Chemistry of Pulp and Papermalting (pub. 1941 by Wiley) (pp. 208- 209). 

1. THE METHOD OF MAKING A BITUMINOUS BINDER FOR FOUNDRY MOLDS AND CORES, WHICH COMPRISES FORMING A MIX CONSISTING ESSENTIALLY OF 40 TO 60 PERENT OF PETROLEUM ASPHALT RESIN, BY WEIGHT, 30TO 55 PERCENT OF COAL TAR PITCH, BY WEIGHT, 3 TO 8 PERCENT OF RESORCINOL, BY WEIGHT, AND 3 TO 10 PERCENT OF THE SOLID CONTENT OF BISULPHITE WASTE LIQUOR, BY WEIGHT, MAINTAINING THE RESULTANT MIX AT A TEMPERATURE OF BETWEEN 300* AND 325*F. FOR AT LEAST 1/2 HOUR, THEN ALLOWING THE RESULTANT MASS TO COOL AND REDUCING THE SAME TO A POWDER. 